diff --git a/security/manager/ssl/security-prefs.js b/security/manager/ssl/security-prefs.js
index 165aefeff1f7..8a3542bb3128 100644
--- a/security/manager/ssl/security-prefs.js
+++ b/security/manager/ssl/security-prefs.js
@@ -28,7 +28,12 @@ pref("security.ssl3.dhe_rsa_aes_128_sha", true);
 pref("security.ssl3.dhe_rsa_aes_256_sha", true);
 pref("security.ssl3.rsa_aes_128_sha", true);
 pref("security.ssl3.rsa_aes_256_sha", true);
+// Deprecate 3DES on nightly builds, Bug 1386754
+#ifdef RELEASE_OR_BETA
 pref("security.ssl3.rsa_des_ede3_sha", true);
+#else
+pref("security.ssl3.rsa_des_ede3_sha", false);
+#endif
 
 pref("security.content.signature.root_hash",
      "97:E8:BA:9C:F1:2F:B3:DE:53:CC:42:A4:E6:57:7E:D6:4D:F4:93:C2:47:B4:14:FE:A0:36:81:8D:38:23:56:0E");